Abstract

Our current studies of the exoskeletal structures and ultrastructures in Lower Devonian dalmanitid trilobites of the Prague Basin are briefly described and discussed. The interior of the exoskeleton in most specimens from the Prague Basin is recrystallised and largely filled with very fine homogeneous sparitic cement. The ultrastructures sensu stricto, e.g., the lamination, layers forming the exoskeleton, and the fine pores or “Osmólska” cavities, are mostly imperceptible even at higher magnifications. However, ultrastructural relics were observed in some polished thin sections and exoskeletal fragments using electron microscopy. Larger structures, especially the eyes, the megapores penetrating the exoskeleton, and the surface sculptures (prosopon sensu Gill 1949), are relatively well preserved and show very fine details. The biological significance of megapores is briefly discussed. Modification of the inner parts of the exoskeletons by diagenetic processes, obscuring most of the fine internal structures, is evident.

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